Human blastoids model blastocyst development and implantation

About one week after fertilization, human embryos implant into the uterus. This necessitates the formation of a blastocyst consisting of a sphere encircling a cavity lodging the embryo proper. Stem cells can form a blastocyst model, which we termed blastoid. Here we show that naive human pluripotent stem cells (PXGL hPSCs) efficiently (>70%) form blastoids generating blastocyst-stage analogs of the 3 founding lineages (>97% trophectoderm, epiblast, and primitive endoderm) according to the sequence and to the pace of blastocyst development. Blastoids form the first axis and we observe that the epiblast induces the maturation of the polar trophectoderm that consequently acquires the specific and transient potential to attach to hormonally-stimulated endometrial cells. Such human blastoids are faithful, scalable, versatile, and ethical models to explore human implantation and development. Refer to individual Series